Forum bmwbike.com

Hi,

What's the method of adjusting the centrifugal governor for an r25/3. I've just replaced the springs and am wondering whether it's possible to adjust it off the bike.

Thanks
Ben

This is a long-winded operation but it can be done.
Firstly ensure the advance/retard unit is in good condidtion and operates freely about the nose of the crank, i.e. springs back to its stop when you hold out the weights and let them go. I take it your new springs are the correct strength?

Set the static timing to the S mark. Use a Xenon strobe light and ensure the S mark is on the timing mark at idle. Take up the revs until the F mark appears in the timing hole. If it does not appear there is inadequate advance, if the mark passes the hole there is too much advance.

Now guestimate how the leaf spring that stops the bobnweights on the advance/ retard unit requires altering. But be careful, too much bending can easily snap the spring!
Refit and try again.

I modified the unit on my R50 to be infinitely adjustable. The spring had broken, so I made a small sliding stop from mild steel and fitted it with a locking screw. I could then adjust the timing accurately without having to remove the unit from the mag. It has worked perfectly for years.

Here is a photo of my /2 advance to which I added a stop bolt. And this raises a question:
Does the leaf spring stop the weights firmly, or does the spring slowly compress and allow the weights to open a bit more?
In other words, should I set the stop bolt close to the spring, or at some distance from the spring as shown in the photo?

Love the mod. Allan.

I would have thought that in view of the lightness of the coil springs and the rigidity of the leaft spring, the weights are stopped dead in their tracks. A strobe light shows that, once the F mark reaches its spot, it stays there and does not "creep" as if the leaf spring is allowing further travel.

If full advance did not exceed the F mark, the stop bolt would not be needed.

The stop bolt was invented by Brian Caro of the Slash 2 Group, to overcome a problem reported with new advance units that exceed the F mark, even when the S mark is correct.

Several of us have added stop bolts to our advances. But I have not experimented enough with the timing light to see if the flat spring is a hard stop or a soft stop.

Further to my last note:

I had the good fortune to pick up a brand new advance/ retard unit recently for a song. I fitted it to my R50 and it is BRILLIANT! Throttle response is ace, so too steady power right through the range. The spring tension is quite clearly critical, so chose replacement springs very carefully and double-check the timing with a multimeter and strobe.